KR20020077506A - Method for obtaining macroscopic fibres and strips from colloidal particles and in particular carbon nanotubes - Google Patents

Abstract

1) The colloidal particles are dispersed in a solvent, optionally using a surfactant,

2) Destabilizing the dispersion of particles by injecting into an external solution stream through one or more orifice openings, preferably under the same temperature and pressure conditions, into an external solution stream that is greater than the viscosity of the dispersion, and optionally aligning the particles. To agglomerate particles into fibers or strips, thereby obtaining fibers and strips from colloidal particles.

Description

METHOD FOR OBTAINING MACROSCOPIC FIBRES AND STRIPS FROM COLLOIDAL PARTICLES AND IN PARTICULAR CARBON NANOTUBES}

The present invention relates to a process for obtaining macrofibers and strips from colloidal particles. More specifically, the present invention relates to a spinning method for obtaining fibers of carbon nanotubes.

According to one embodiment of the invention, the invention relates to the macroscopic fibers and strips produced from colloidal particles which can be anisotropic.

Carbon nanotubes have excellent physical properties, and in various fields, in particular in the electronics industry (depending on their temperature and structure, they can be conductors, semiconductors or insulators), in the field of mechanical engineering, for example as a reinforcement of composites. (Nanotubes are 100 times stronger and 6 times lighter than steel) and in the field of electrical engineering (which can be made to expand or contract by applying a charge).

Unfortunately, however, the major drawback in this current industrial application is that there are no macroscopic formulations with controlled structures.

The production of such nanotubes as macroscopic fibers or strips greatly facilitates their handling (transportation, storage, etc.), making the nanotubes more useful for the applications described above.

Thus, carbon fibers, especially used in the composites industry, are obtained by conventional methods by spinning methods of viscoelastic mixtures. These are produced, for example, by drawing the heated carbon pitch directly to draw the viscoelastic polymer or to make it viscoelastic, followed by carbonization by heating. While this technique is very common, it can also be applied to plastics, glass or metals.

In contrast, such high temperature processes are not applicable to colloidal particle-containing solutions, since there is a risk of causing decomposition of the solvent. This is also not applicable to carbon nanotubes, since the heating of carbon nanotubes causes the carbon nanotubes to degrade before they reach a viscoelastic state.

It is therefore an object of the present invention to overcome the aforementioned disadvantages by proposing a method of obtaining macrofibers and strips, in particular carbon nanotubes, from colloidal particles dispersed in solution. The invention also relates to the fibers and strips thus obtained.

For this purpose, the method of obtaining fibers and strips from the colloidal particles according to the invention

1) Colloidal particles are dispersed in a solvent, optionally using a surfactant,

2) Destabilizing the dispersion of particles by injection into at least one orifice opening into an external solution, preferably by measuring the viscosity under the same temperature and pressure conditions and into an external solution larger than the viscosity of the dispersion obtained in 1), By aligning the particles so as to aggregate the particles into fibers or strips.

Other features and advantages of the invention will be apparent from the following detailed description with reference to the accompanying drawings, which are illustrated by way of example, which should not be construed as limiting the invention in any way. In the drawing,

1 is a schematic side view showing a schematic example of an experimental device for applying a second step of the method according to the invention.

2 is a series of photographs showing the formation of knots from twisted nanotube fibers obtained by the method according to the invention.

3a to 3c show photographs of strips of carbon nanotubes obtained by the method according to the invention and observed between an analyzer and a polarizer crossed by an optical microscope.

According to a preferred embodiment of the invention, the method of obtaining the macrofibers and strips from the colloidal particles comprises at least two steps.

The first step consists in dispersing the colloidal particles, in particular nanotubes, in an aqueous or organic solution. To this end, particles having hydrophobic properties are dispersed using surfactants commonly used to disperse hydrophobic particles in a solvent such as water or an alcohol such as ethanol, optionally such a solvent. In the case of using surfactants, coating the particles can prevent their agglomeration, so that their dispersions are stable. If the solvent used is water, the dispersion can be obtained using various anionic, cationic or neutral molecular or polymeric surfactants such as sodium dodecyl sulfate (SDS), alkaryl esters or tetradecyltrimethylammonium bromide. . Depending on the nature of the formulation used, its concentration will be in the range of 1% to several%.

The initial dispersion of the colloidal particles, for example nanotubes, should be as homogeneous as possible. The degree of homogenization can be tested by a simple and conventional method by optical microscopy, which easily detects the presence of heterogeneities which have occurred due to the presence of aggregates of particles to be optically detected.

Strips or fibers formed using a thinner dispersion of colloidal particles are very brittle and difficult to handle for conversion into threads. It is also difficult to produce strips and fibers using more concentrated suspensions, because it is difficult to obtain homogeneous concentrated dispersions. However, it is always desirable to use the suspension as concentrated as possible while keeping the suspension homogeneous.

Using raw nanotubes synthesized by an electric arc, it is advantageous to use concentrates of water, from 0.3 to 0.5% by weight of nanotubes and from 1 to 1.5% by weight of SDS dispersant as solvents for the preparation of the initial dispersion.

Using nanotubes prepared by the HiPco method is easier to use than nanotubes synthesized by electric arc, and can be used, for example, at concentrations as low as 0.1 wt%.

In general, the dispersion is preferably formulated using an ultrasonic homogenizer. Using a homogenizer that directly immerses the probe in the dispersion is much faster and more efficient than using an ultrasonic bath. Typically the power of the ultrasonic bath is too low to produce a homogeneous and relatively concentrated dispersion of particles.

The second step of the process according to the invention is to measure the viscosity under the same temperature and pressure conditions to cause the colloidal particles to be aligned in the direction initially added by the external solution stream due to tension, so that the viscosity is higher than the viscosity of the dispersion. It is preferred that the higher the laminar flow of the external solution consists of injecting the aqueous or organic dispersion of the particles obtained after the first step through the one or more orifice openings. To achieve this result, polymers which can be polyols or polyalcohols (eg polyvinyl alcohol, alginate or cellulose) or minerals (eg clay) can be used as viscosity regulators of the external solution.

In addition, the external solution should preferably contain chemicals that can cause agglomeration (or entanglement) of dispersed particles, especially polymers that can produce a crosslinking effect.

Thus, an aqueous or organic dispersion of the particles containing the surfactant can be injected through the orifice into the external solution and the adsorbed molecules of the surfactant can be replaced with a flocculant or viscosity modifier of the external solution, after which the particles are no longer stabilized. Thus, at the outlet of the orifice, an agglomerate is formed to form a strip or fiber whose cross section is determined according to the cross section of the orifice used. More simply, the agglomeration of the particles can be induced by desorption of the surfactant. In addition, even though the surfactant remains adsorbed, these particles may aggregate in the presence of a flocculant.

Examples of flocculants that can be used include polyvinyl alcohol, chitosan, weakly charged polyelectrolytes such as copolymers of acrylamide and acrylic acid (which also serve as viscosity modifiers), salts (Na ⁺ Cl ⁻ , K ⁺ Cl ⁻ ) or And surfactants that are charged or neutral as opposed to the charge of the formulation used to disperse the particles in the first step of the process when the particles are anionic.

Higher molecular weight PVA is generally used (at least 100,000 g / mol) to impart better cohesion to the strip or to the fibers. It is advantageous to use water-soluble PVA having a molecular weight of 10,000 or more, in particular 10,000 to 200,000. The efficiency seems to increase with the polymer size from the fact that the aggregation of the particles is due to the so-called "crosslinking" effect of the particles by PVA.

Low molecular weight (about 10,000 to 15,000 g / mol) PVA can be used at high concentrations because of its faster dissolution and less viscosity increase of the solution.

This has the advantage that absorption can be achieved quickly and can be more easily desorbed than high molecular weight polymers. However, strips and fibers break more easily, which does not appear to be very effective in forming crosslinks.

If they are not homogeneous, it may be considered necessary to filter the PVA solution.

According to an advantageous feature of the invention, the obtained fibers or strips can be cleaned using a rinse product at the end of the second stage in order to completely desorb the external solution and dispersant. In particular, this step can consist of a continuous rinse with pure water.

In addition, the density of the fibers and strips can be controlled by the concentration of the initial dispersion of the particles. For example, for carbon nanotubes, it is common for the weight fraction to be less than several percent.

According to another advantageous feature of the invention, this method comprises a final step consisting of densifying the macroscopic fibers and strips.

Therefore, carrying out this final step consists in slowly drawing the fibers or stripping them from the rinse product (especially water). Thus, capillary contraction occurs when such fibers or strips are removed from the solvent, which causes primary densification, which is increased by evaporation of the solvent.

The applicant intends to explain various variables used in the method according to the invention.

The first step consists of the complete mixing of the colloidal particles and the solvent (aqueous or organic) to obtain a solution having the properties of the dispersion.

In order to meet the various constraints of the second step of this method, various types of devices may be suitable, such as batch operated devices or vice versa continuously operated devices.

Thus, according to the first class of devices, the reactor or vessel comprises an external solution, which is rotated by operation, in particular by means of a motor (for example a rotating plate). Such containers may also be equipped with a double jacket to allow the heat-transfer fluid to be circulated to change the temperature of the external solution and thus change the physicochemical parameters (eg, viscosity, etc.).

By regulating the rotational speed of the motor, the medium imparts optimum hydraulic pressure conditions, especially in terms of speed and flow rate, so as to accompany the aqueous or organic dispersions released through the plurality of orifices located in the circulation of the external solution.

Orifices of varying cross-sectional profiles (rectangular, cylindrical, square, conical, etc.) are connected by pipeline to another tank containing an aqueous or organic dispersion. In addition, the metering pump and / or centrifuge may be mounted in a supply circuit between the buffer tank containing the dispersion and the separation tank in the external solution, depending on the operating parameters of the pump (rotational speed, delivery pressure, flow rate, etc.). Optimum pressure conditions should be given to (aqueous or organic).

In a continuously operated apparatus, the characteristics of the circuit for supplying the dispersion are the same as those of the batch operated apparatus. Devices of this known type can be used in the textile industry or characterized for the spinning of polymers.

In contrast, a vessel containing an external solution is provided with an inlet orifice and an outlet orifice which is discharged after the external solution has been introduced, which is optionally by a pressurization circuit (pump, buffer tank, etc.) and optionally by a return circuit, including pump or circulation means. By virtue of the circulation of the dispersion and hence the accompanying conditions.

Of course, all of these devices, whether operated batchwise or continuously, can be controlled by an automated system or a computer controlled process operating unit such that the user can provide information relating to the separation process in order to obtain optimum operating conditions.

Thus, the higher the viscosity of the external solution for aqueous or organic dispersions (under the same temperature and pressure conditions), the smaller the corrected orifice size, the higher the flow rate of the external solution, the greater the tension, The alignment becomes more pronounced. For example, the use of viscous external solutions and fine orifices flowing at high speed creates anisotropic structures. Conversely, the use of slow flowing low viscosity external solutions and large cross sections creates fibers and strips with little or no particle alignment.

During this step, it is desirable to remain within the laminar flow conditions. Too fast flow and turbulence will result in no long and uniform fibers or strips.

An aqueous solution of polyvinyl alcohol (PVA) is effective for destabilizing the suspension of particles and causing their aggregation. In addition, PVA is a polymer that greatly increases the viscosity of the solution to promote laminar flow.

The most readily available tubes for the injection of dispersions of particles are cylinders or needles. It is possible to use a tube having a diameter of 0.5 to 1.0 mm. If the dispersion of particles and the PVA solution are satisfied with each other, it is preferable to choose a tube with a thin wall thickness so as not to generate turbulence.

In the case of nanotubes synthesized by an electric arc, the dispersion is injected through a cylindrical tube with a diameter of 0.7 mm, the injection rate used is 0.8 to 2.5 cm 3 / min, and the flow rate of the PVA solution in the nanotube injection is 5 to 30 m / min.

Low injection rates and high flow rates of PVA solutions result in strong tensions that draw the strip or fiber. Thus, the strips or fibers become thinner and the alignment of the nanotubes becomes more pronounced. However, if the tension is too large, it has the disadvantage of being too thin and making the strip or fiber more brittle. It is also important not to use too fast flow rates to prevent turbulent conditions.

High injection rates and low flow rates are thicker and thus produce harder strips or fibers. Such conditions will promote the production of fibers. However, these conditions do not promote the alignment of the nanotubes in the strip or fiber.

HiPco nanotubes can be used at high speeds while maintaining the good mechanical properties of the strip or fiber.

Finally, the method according to the invention can generally be applied to colloidal particles, in particular to anisotropic particles (e.g. nanotubes such as carbon, tungsten sulfide, boron nitride, clay flakes, cellulose, whiskers, silicon carbide whiskers, etc.). have.

With regard to the densification step of the strip or fiber, when the strip or fiber is discharged vertically from water, the drying rate tends to be faster if drawn very quickly. This may allow more water contained in the strip or fiber to be transported. As a result, subsequent drainage and drying is rapid.

In contrast, the discharge must be made slow enough to avoid treating the strip or fibers with high tension that may rupture the strip or fibers.

The maximum discharge rate is highly dependent on the size and properties of the strip or fiber and the nature of the particles. If not constrained in time, it is desirable to slow the discharge so that the strip or fiber does not break. The small tension created therefrom is not optimal for particle alignment, but other operations are possible to aid alignment in strips or fibers. It is also possible to deliver the rinsed strips or fibers to a solvent that is more volatile than water (eg alcohol or acetone) in order to dry more quickly during discharge.

The manipulation of rinsing and washing with pure water makes it impossible to desorb the largest molecule of flocculant such as PVA within a reasonable time (days). Thus, the residue of the flocculant stays in the final strip or fiber. This has important consequences for the strip or fiber formed. When the strip or fibers are immersed again in water they will partially swell. Its length spontaneously increases to several percent, and its diameter doubles.

For example, the effect of PVA (or other flocculant) can be prevented by annealing at high temperatures (400 ° C. or higher) at which PVA decomposes.

In addition, the strip or fibers may be annealed at an appropriate temperature (temperature below 300 ° C.) to melt the viscosity modifier, such as PVA, without degradation. In addition, the drawing of fibers under these conditions improves the alignment of the particles.

Such annealing is advantageously accompanied by further addition of polymers and / or plasticizers. Addition at such high temperatures makes it possible to obtain coated strips or fibers.

Typically, the structure and properties of the strips or fibers can be modified by the mechanical action (especially tension and distortion) exerted thereon. This operation is preferably performed on less brittle materials than the fibers obtained directly after rinsing and drying. This operation can be easily performed on the initial strip or fiber in the presence of molten polymer or elastomer at high temperatures or during annealing.

In addition, manipulation of the condensation and drying of the strips or fibers can separate the impurities and colloidal particles present. Impurities such as amorphous carbon or graphite tend to form external envelopes, for example, around a cylinder consisting primarily of nanotubes.

This phenomenon can be used to make new materials. Particles of μm or nm size may be deliberately added to an external solution comprising strips or fibers. This particle is then entrained during drawing the strip or fiber to form the final strip or fiber. When using particles that exhibit a pattern such as carbon containing impurities, they form an outer envelope around the strip or fiber of colloidal particles. This effect can be used, for example, to create thin envelopes that separate the polymer around strips or fibers of colloidal particles using latex particles.

Various types of envelopes can be obtained using other types of particles in any type of strip or fiber according to the present invention.

Separation of particles and strips or fibers is believed to occur due to lateral drainage of the solvent during the discharge and drawing of the strips or fibers. If the strip or fiber is discharged from the solvent, the drainage will be accompanied by particles at its periphery. Concentration at the periphery causes the particles to form an outer envelope around the core of the strip or fiber. This phenomenon is observed in any system that includes strips or fibers formed from or from polymers in the presence of other particles of as many different forms as possible, where little or no bond is attached to the polymers or particles forming the fibers. . The lack of or weak bonding between the particles and the strips or fibers can be drained to separate the various components, resulting in strips or fibers formed from envelopes and cores having different properties.

Thus, a strip or fiber comprising an envelope is obtained, and particles having a size of μm or nm around the strip or fiber are formed by the drying around.

The schematic diagram of the experimental set-up for carrying out the second step of the method using the solution of carbon nanotubes dispersed in water in the first step as a starting material will be described.

As shown in FIG. 1, such a device in particular comprises a syringe 1 or an equivalent, in which an aqueous solution of nanotubes dispersed in the first step is placed. For this purpose, the capillary tube 2 having a very flat cross section fixed to the syringe presses the piston 3 of the syringe to release the solution into the provided cylindrical container 4. The injection rate is in the range of 1 cm 3 to several cm 3 per minute.

The cylindrical container 4 having a very flat side is fixed on a plate (not shown) which is allowed to rotate at variable speeds of tens to hundreds of rpm. The outlet end of the capillary 2 is immersed in an external solution 5 (preferably high speed) contained in the vessel. In particular, the outlet end of the capillary tube is arranged to be in contact with the container 4 spaced apart from the axis of rotation. A dispersion of low viscosity nanotubes is then entrained under tension by the solution 5 at the outlet of the capillary tube to align the nanotubes in the flow direction.

In fact, the dispersed nanotube solution comprising the surfactant is injected into the viscous liquid 5 through the capillary 2 by the syringe 1, and the molecules of the surfactant are replaced with the viscosity regulator of the solution 5. In addition, since the nanotubes are not stabilized by the coagulant of the external solution 5, they aggregate upon release from the capillary 2 to form strips or fibers 6 whose cross section is determined by the cross section of the capillary tube used. do.

The features of the macrofibers and strips according to the invention obtained from colloidal particles, which are optionally anisotropic, in particular from carbon nanotubes, are described below.

These carbon fibers and strips consist of tangled nanotubes. This structure makes the fibers significantly flexible while maintaining good mechanical properties under tension due to the alignment of the carbon in the form of graphite cylinders in the nanotubes. For example, as shown in FIG. 2, the fibers may be largely curved to form a knot or weave.

In addition, these fibers are very fine and dense. For example, it is possible to obtain a fiber having a variable length of 1 to 100 microns in diameter, the density of which can reach about 1.5 g / cm 3, where density is the theoretical value (1.3 g / cm 3) for dense lamination of nanotubes. Is close to).

In addition, the obtained fibers and strips may have an anisotropic structure in which the nanotubes have a preferential orientation. This orientation is an important variable for expanding the electrical and mechanical response of a given material. This structural anisotropy can thus be tested by optical microscopy between crossed polarizers. Thus, it can be clearly seen in FIGS. 3A-3C that the intensity transmitted by the strip can vary depending on the orientation of the polarizer's axis.

In the photographs of FIGS. 3A-3C, the axes of the polarizer and the analyzer are the vertical axis and the horizontal axis, respectively. For example, in FIG. 3A, the strip is parallel to the polarizer and no light passes through it. The same applies to FIG. 3C, where the strip is parallel to the analyzer. In contrast, the strip is inclined 45 ° with respect to the polarizer and the analyzer (FIG. 3B), where the analyzer allows some of the light to pass through. This represents the preferential alignment of the carbon nanotubes along the major axis of the strip, ie in the direction initially added by the flow of the external solution.

In addition, the nanotubes can yield fibers or strips that, for example, have little alignment along the major axis of the fibers or strips, if necessary. For this purpose, the external solution used during the second step of the process according to the invention should have a low viscosity with respect to the aqueous dispersion of nanotubes under the same temperature and pressure conditions, its flow rate should be slow and the extrusion orifice It must be wide.

In order to obtain a final product with improved mechanical and electrical properties compared to the prior art, "single wall" carbon nanotubes (ie, consisting of a single graphite cylinder) or "multiwall" carbon nanotubes (which can be Consisting of two coaxial graphite cylinders), single-walled nanotubes have superior mechanical and electrical properties compared to multi-walled nanotubes, but are expensive to produce.

According to an advantageous feature of the invention, the carbon nanotubes used in the dispersion are chemically modified by grafts of molecular groups, for example polyethyl glycol groups or acid groups. Such grafts can increase the bonds (van der Waals type bonds, hydrophobic bonds or hydrogen bonds) between the fibers or strips obtained, which has the advantage of strengthening the material consisting of these fibers or strips.

The fibers or strips according to the invention have a porosity in which particles, for example carbon or polymer, can be introduced into these voids. In addition, the introduction of such particles is excellent in resistance to mechanical stress, it is possible to obtain a fiber excellent in aggregation.

According to another advantageous feature of the invention, fibers obtained from carbon nanotubes are used to reinforce materials, in particular composites and cables. In fact, these fibers have the usual characteristics of carbon (heat resistance, chemical resistance, strength of atomic bonds in the graphite layer), but become less brittle when distorted. This allows the production of highly flexible composites, even cables or fabrics consisting only of carbon nanotubes.

According to another advantageous feature of the invention, fibers and strips obtained from carbon nanotubes are used as conductors, semiconductors or insulators depending on their structure and their temperature in the field of electronics and microelectronics.

According to another advantageous feature of the invention, the fibers and strips obtained from carbon nanotubes are used as systems (eg displays) for electron emission by nanotubes.

According to another advantageous feature of the invention, the fibers and strips obtained from carbon nanotubes are used as electrodynamic actuators or artificial muscles for various mechanical systems. Thus, films of randomly oriented single-walled carbon nanotubes undergo mechanical deformation under the influence of electricity, which is amplified with the aligned system. Typically, such fibers or strips can be used in devices that convert electrical energy into mechanical energy (or vice versa).

As catalyst or catalyst support in chemical reactions, as electrode in electrochemistry, for hydrogen storage in battery systems (especially for fibers made of carbon nanotubes), for near-field microscopy (tunnel effects and atomic force microscopy) As a tip, as a filter membrane, as a chemical detector (the electrical resistance of carbon fibers varies with respect to the chemical environment) or in an optical or electro-optical device (electrodiffusion, optical limitation, etc.), or in a biological material (prosthesis, gun, ligament Applications of fibers and strips can be considered in the use for the production of).

Finally, it is possible to use the fibers or strips of the invention as a transformant of mechanical energy into electrical energy and vice versa. In fact, the mechanical stress of such fibers or strips causes the appearance of electrical charges in them, and the fibers or strips under electrical influence are deformed. Examples of such applications include mechanical stress sensors, sound wave sensors, ultrasonic sensors, and the like.

It is also contemplated to use the fibers or strips according to the invention to produce electrochemical detectors and / or electrodes.

The present invention as described above provides a number of advantages, and in particular, such a method can yield fibers from particles such as carbon nanotubes or from particles generally dispersed in solution.

Claims (27)

1) Colloidal particles are dispersed in a solvent, optionally using a surfactant, 2) Destabilizing the dispersion of the particles by injection into an external solution stream through one or more orifice openings, preferably under the same temperature and pressure conditions, into an external solution stream having a viscosity greater than that of the dispersion obtained in 1). To agglomerate the particles into fibers or strips by optionally aligning the particles. The method of claim 1 wherein the particles are dispersed in an aqueous or organic solvent using anionic, cationic or neutral molecular or polymeric surfactants. 3. Process according to claim 1 or 2, characterized in that the external solution comprises a viscosity modifier selected from polymers such as polyols or polyalcohols, in particular polyvinyl alcohol or cellulose or minerals such as clays. 4. The flocculant of claim 3, wherein the flocculant is added to the external solution, and the flocculant has an opposite charge or neutral interface with the polymer capable of producing the crosslinking effect, and the agent used to disperse the particles if the particles are ionic. Characterized in that it is selected from an active agent or a salt. The method of claim 4 wherein the polymer consists of polyvinyl alcohol. 6. The process according to claim 5, wherein the polyvinyl alcohol has a molecular weight of at least 10,000, in particular 10,000 to 200,000. The fiber or strip of claim 1, wherein the fiber or strip is densified by capillary contraction and / or the obtained fiber or strip uses a rinse product to desorb the external solution and / or surfactant. By washing. 8. The method of claim 7, wherein the fiber or strip is discharged vertically from the rinse product. 8. Process according to claim 7, characterized in that the fibers or strips are carried out at high temperatures, in particular at temperatures above 400 ° C or at intermediate temperatures, in particular at temperatures below 300 ° C. The method according to claim 7 or 8, wherein the fibers or strips are subjected to mechanical action during annealing, optionally with addition of polymers and / or plasticizers. The method of claim 1, wherein the external solution comprises particles of μm or nm size to form an outer envelope around the fiber or strip. The method according to claim 1, wherein the solution of the dispersion is injected through at least one orifice having a cross section of a shape corresponding to the desired shape, in particular for the fiber or strip. The method according to claim 1, wherein the nanotubes, in particular carbon nanotubes, are used as colloidal particles. Fibers and strips characterized in that they consist of colloidal particles, in particular carbon nanotubes. 15. The fiber and strip of claim 14 having an anisotropic structure as measured by an optical microscope between crossed polarizers. 16. The fibers and strips according to claim 14 or 15, which are largely curved to form a knot or to weave. The fiber and strip according to any one of claims 14 to 16, having a diameter of 1 to 100 μm. 18. The fiber and strip of claim 14 or 17, wherein the particles are carbon nanotubes that are chemically modified by grafts of chemical groups and / or consist of single or multiple coaxial cylinders of graphite. 19. The fibers and strips of any one of claims 14-18, wherein the density can be up to about 1.5 g / cm 3. 20. The fiber and strip according to any one of claims 14 to 19, having an outer envelope formed by ambient drying around the strip and the fiber having a particle size of μm or nm. Use of fibers and strips according to any of claims 14 to 20 for reinforcement of materials consisting of fibers, strips or cables. Use of fibers and strips according to any of claims 14 to 20 for the manufacture of conductors, semiconductors and insulators in electronics or microelectronics. Use of the fibers and strips according to any one of claims 14 to 20 as electron emission systems, in particular as display systems. Use of the fibers and strips according to any of claims 14 to 20 as artificial muscle or electromechanical actuators. Use of fibers and strips according to any one of claims 14 to 20 for the production of materials such as fabrics or cables. Use of the fibers and strips according to any one of claims 14 to 20 as a transformation of mechanical energy into electrical energy and vice versa. Use of fibers and strips according to any of claims 14 to 20 for the manufacture of chemical detectors and / or electrodes.